Non-stop mode for Windows (mingw)

[Raphael Zulliger]

According to empirical tests and by looking at the GDB sources, 
'windows-nat.c' and, therefore, GDB running on Windows (mingw) does not 
support non-stop debugging.

- What's the technical reason behind this? Was it just not ported to 
that platform so far? Wasn't it done because it's tricky?
- What would be needed to support it? (Is the main required thing that 
'displaced single stepping' is required for non-stop mode?)

Thanks!
Raphael